The present invention, in some embodiments thereof, relates to neuron stimulation and, more particularly, but not exclusively, to light induced neuron stimulation.
A neuroprosthesis is a device which is designed for replacing or improving the function of an impaired nervous system or sensory organ. Known in the art are neuroprosthesis for the treatment of functional disorders of the visual system, hearing system, cranial nerve system, spinal cord and peripheral nervous system [to this end see, e.g., International Patent Publication Nos. 98/036793 and WO 98/036795, and U.S. Pat. Nos. 6,393,327, 6,497,699, 6,829,510 and 7,447,548].
A visual prosthesis, for example, is a device that captures aspects of the visual environment and uses this information to stimulate nerves within the visual pathway to influence vision. A visual prosthesis may be placed within the eye or at some location on the path toward or within the visual part of the brain. Visual prosthetic devices within the eye can be positioned on the inner surface of the retina (i.e., epi-retinal) or under the retina (sub-retinal).
An auditory prosthesis is a device that delivers stimuli representative of sound to the spiral ganglion which is responsible for transmitting impulses from the inner ear to the brain. Also known are auditory prostheses that deliver stimuli directly to the auditory cortex or the auditory brainstem.
A neuroprosthesis operates by interacting with neurons. A neuron consists of: a branched pattern of processes, commonly known as dendrites, which act to receive information; a cell body, known as the soma, from which the dendrites extend, and which integrates the received information and provides for the metabolic needs of the neuron; and an axon extending from the soma, for transporting constituents between the soma and distant synapses, which transfer information to the next set of nerve dendrites.
When no stimulation is presented, the neuron is negatively polarized inside the soma membrane with respect to the outside of the membrane. Depolarization of a soma membrane creates an action potential, which effectively travels via axons, e.g., to the inner brain, thereby sending the stimulation signal thereto. Thus, information is represented in the nervous system as a series of action potentials that travel between the neurons via the membranes of axons.
Once stimulated, the neuron generates and allows propagation of an electrical impulse therein. Various techniques have been utilized for stimulating neurons. These include electrical stimulation, mechanical stimulation, thermal stimulation, chemical stimulation and optical stimulation. In the field of neuroprosthesis, the most common stimulation technique is electrical stimulation wherein a transient current or voltage pulse is applied via electrodes. For example, many visual prostheses include epi-retinal or sub-retinal microelectrode array implants, manufactured using micro-fabrication technology borrowed from the semiconductor industry.
Published Application No. 20030208245 discloses a technique for directly stimulating neural tissue with optical energy. An optical field having a wavelength of 1-6 μm is focused on a target neural tissue such that the target neural tissue propagates an electrical impulse. The focusing is onto an area of 50-600 μm micrometers.
U.S. Published Application No. 20060161227 discloses a system for stimulating auditory neurons associated with the spiral ganglion cells. Optical energy at a wavelength of 0.5-10 μm is delivered along an optical path to a target site of auditory neurons to evoke compound action potential therein. The evoked action potential is monitored by monitoring means.
The light sources used in the above publications are laser devices, and the produced optical energy is absorbed by the tissue's water content within a typical absorption distance of several hundred microns, allowing the optical field to directly interact with the tissue. It has been hypothesized [Wells et al., “Biophysical mechanisms of transient optical stimulation of peripheral nerve,” Biophys J 93, 2567-80 (2007)] that the photobiological effect of light absorption on the tissue is mediated through a photo-thermal mechanism, rather than electrical field, photochemical or photomechanical mechanisms.
A system capable of patterned activation of many neurons with millisecond precision using rapid UV laser deflection has recently been disclosed [Shoham et al., “Rapid neurotransmitter uncaging in spatially defined patterns,” Nature Methods 2, 837-843 (2005)]. In this system, UV light is used to activate neurons by uncaging glutamate, the major excitatory neurotransmitter in the central nervous system.
Recently, retinal ganglion cells have been directly activated by artificially causing them to express Channelrhodopsin II (ChR2), a light-gated cation channel [Reutsky et al., “Patterned optical activation of Channelrhodopsin II expressing retinal ganglion cells,” in CNE '07. 3rd International IEEE/EMBS Conference on Neural Engineering, 2007 50-52 (2007)]. Patterned stimulation of the cells was demonstrated by means of video projection technology based on a Texas Instruments Digital Minor Device.
Additional background art includes Wells et al. “Optical stimulation of neural tissue in vivo,” Opt Lett 30, 504-6 (2005); Pappas et al., “Nanoscale Engineering of a Cellular Interface with Semiconductor Nanoparticle Films for Photoelectric Stimulation of Neurons,” Nano Letters (2007) Vol. 7, No. 2, 513-519 and Izzo et al., “Laser stimulation of the auditory nerve,” Lasers Surg Med 38, 745-53 (2006); U.S. Published Application Nos. 20060161227 and 20030208245].